class Solution {//leetcode413——等差数列划分
public:
    int numberOfArithmeticSlices(vector<int>& nums) {
        int n=nums.size();
        if(n<3) return 0;
        vector<int> dp(n);
        int ret=0;
        for(int i=2;i<n;i++){
            if((nums[i]-nums[i-1])==(nums[i-1]-nums[i-2]))
                dp[i]=dp[i-1]+1;
            ret+=dp[i];
        }
        return ret;
    }
};